1. Field of the Invention
The present invention relates to a lens apparatus capable of attaching an optical accessory on an object side thereof.
2. Description of the Related Art
In general, a lens apparatus of an image pickup apparatus such as a camera or a video camera has an object-side end of a lens barrel protruded beyond a lens on a foremost surface toward an object side in order to protect the lens from damages when the lens apparatus is placed on something. Hereinbelow, the lens barrel protruded beyond the foremost lens toward the object side is referred to as a lens protection lens barrel.
Conventionally, optical accessories to be attached to a front side (object side) of such lens apparatus are commercially available and, for example, an optical filter, a teleconverter, a wide converter, a wide attachment, a fisheye attachment, and a close-up lens are well known (for example, Japanese Patent Application Laid-Open No. 2001-333315). The optical accessories include an optical accessory in which an outer diameter of an optical element in a rearmost portion is larger than that of the lens protection lens barrel. The optical accessory is designed so as to avoid interference between the optical element and the lens apparatus when the optical accessory is attached to the lens apparatus.
The attachment of the optical accessory to the lens apparatus is described hereinbelow referring to the attachment of an optical filter to the lens apparatus as an example. The attachment of the optical filter to the lens apparatus is performed via an optical accessory support lens barrel. An outer peripheral portion of the optical filter and an inner peripheral portion of the optical accessory support lens barrel are provided with screw portions, and the optical filter is fixed to the optical accessory support lens barrel by screwing the screw portions together. An inner diameter of an attachment portion of the optical accessory support lens barrel and an outer diameter of an optical accessory attachment portion of the lens apparatus are substantially identical to each other. At the time of the attachment, the optical accessory support lens barrel is firstly inserted from the front side of the lens apparatus. Subsequently, when a rear end of the optical accessory support lens barrel comes in contact with a flange portion of an outer peripheral portion of the lens apparatus, a locking screw of the optical accessory support lens barrel is tightened. On the inner diameter side of the attachment portion of the optical accessory support lens barrel, an arc-shaped locking member having one end fixed to the optical accessory support lens barrel is disposed, and a part of the locking member, which is pressed to be elastically deformed when the locking screw is tightened, is engaged with a groove provided in an outer periphery of the lens apparatus, and the optical accessory support lens barrel can be thereby fixed to the lens apparatus.
On the other hand, there is proposed an image pickup apparatus including a retractable lens apparatus as a part thereof in which a switch for detecting attachment of an optical accessory support lens barrel capable of attaching an optical accessory on the front side thereof is provided, and the position of an object-side end of the retractable lens apparatus is limited to a range rearward of a rear end of an optical element of the optical accessory based on the operation of the detection switch (for example, Japanese Patent Application Laid-Open No. 2004-333778).
In general, in order to prevent the occurrence of vignetting in a shooting optical system in which the optical accessory is attached to the lens apparatus, as an interval between the foremost lens of the lens apparatus and the optical element of the optical accessory increases, a radial dimension of the optical element of the optical accessory needs to be increased correspondingly. However, among optical accessories, there is an optical accessory in which it is difficult to reduce the interval between the optical element of the optical accessory and the foremost lens of the lens apparatus due to a restriction resulting from interference between the optical element and the object-side end of the lens protection lens barrel of the lens apparatus. This condition applies to many of the optical accessories each having the outer diameter of the optical element in the rearmost portion larger than the outer diameter of the lens protection lens barrel. Consequently, there has been the problem in that increases in size and weight of such optical accessories to be attached to conventional lens apparatuses are inevitable.
Japanese Patent Application Laid-Open No. 2004-333778 discloses a method of reducing the size of an optical accessory by reducing an interval between the foremost surface of the lens apparatus and the optical accessory with its use limited to a wide-side zoom range shorter than conventional intervals. However, the lens apparatus is limited to the retractable lens apparatus in which the foremost surface moves back and forth during zooming, and the method is not applicable to optical accessories in general.